Brain ischemia is a leading cause of morbidity and mortality in the United States. We seek to develop therapeutics to reduce the extent of damage and functional impairment resulting from ischemic injury to the brain, an area of significant unmet medical need. In a mouse model of stroke injury we have demonstrated that the synthetic dsRNA, polyinosinic-polycytidylic acid stabilized by poly-L-lysine and carboxymethylcellulose (PIC, Hiltonol), is a robust prophylactic neuroprotectant against ischemic injury. PIC given to mice one day prior to transient middle cerebral artery occlusion reduced the area of damage in the brain by ~95%. We recently published that interferon (IFN) receptor signaling is required for PIC-induced neuroprotection against mouse stroke, providing a potential mechanistic biomarker for predicting neuroprotective doses. Based on our studies in mice, we hypothesize that preconditioning is mediated through systemic IFN secretion and consequent induction of interferon regulated genes in the brain and that these markers can be used to identify efficacious doses for translation to non-human primates (NHP) studies and ultimately human clinical trials. R21 Specific Aims: Aim 1. Validate biomarkers in rhesus macaques that best reflect PIC bioactivity induced by efficacious doses in the mouse. Milestone Define a dose of PIC that results in the induction of the mechanistic biomarker IFN? and at least 3 of the 4 other cytokine biomarkers in the NHP to levels within the interquartile range (25th-75th percentile) of fold changes seen in the mouse at efficacious doses. If we fail to identify a dose that meets both conditions we will rely solely on induction of the mechanistic biomarker IFN?. R21 Criteria for Success. The primary goal is to establish a neuroprotective dose across species based on the induction of systemic biomarkers associated with efficacious doses. A no-go decision will be reached if we fail to identify a dose of PIC that result in an increase of the mechanistic biomarker, IFN?. R33 Specific Aim: Aim 1. Evaluate the potential of PIC to protect against cerebral ischemic injury in NHPs. Milestone 1) Establish a dose that demonstrates a >25% reduction in neurological score in a majority of animals preconditioned with PIC and/or >25% reduction in infarct volume (T2 magnetic resonance images;? day 2). We view this milestone as essential for progression of PIC to clinical preconditioning studies. 2) Establish a clinical monitoring strategy of biomarkers that correlate with improved outcomes. A biomarker strategy would greatly reduce the risk of failure in clinical studies by providing a means to better establish target doses in populations with significant co-morbidities.